Generally, in order to generate electric power in a fuel cell stack, hydrogen ions must transfer to a cathode through a membrane. Also, the membrane must be humid for the transferring of the hydrogen ions.
When the hydrogen ions transfer to the cathode, the hydrogen ions take water molecules. Therefore, in order to maintain the humidity of the membrane at an appropriate level, it is needed to humidify hydrogen that is supplied to the fuel cell stack.
There are two general methods for humidifying the hydrogen: one is an internal humidifying method in which humidifying is performed within the fuel cell stack, and the other is an external humidifying method in which the hydrogen is humidified outside of the fuel cell stack.
The internal humidifying method has various advantages because it makes it possible to simultaneously generate electric power and humidify of the hydrogen within the fuel cell stack so that a fuel cell stack can be easily installed in a vehicle.
In the external humidifying method, a humidifier includes a vibrator converting water into vapor, and a blower that transfers the vapor to a hydrogen supply line and an air supply line. According to operational condition changes, amounts of generated vapor and transferred vapor are controlled, thereby supplying optimal humidity to the membrane.
In such a prior humidifying system, the vapors generated by the vibrator and supplied to the hydrogen supply line and the air supply line require a plurality of blowers. This increases power consumption and requires separate control logic.
Furthermore, to control the amounts of generated vapor and transferred vapor, a plurality of control logic paths and control circuits are needed. Therefore, optimization of the control logic becomes very difficult.
Still further, a temperature drop caused by a pressure drop of the hydrogen and caused by the mixing of vapors with hydrogen and air cannot be compensated.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known to a person skilled in the art.